The invention relates generally to the field of wireless communications and two-way wireless communications systems. More particularly, the invention relates to the detection of duplicate messages and correction of erred messages in a wireless communication device, such as a two-way pager.
Communications systems generally transfer information between a source and a destination. Typically a communication system includes a transmitter and a receiver which transmit and receive information signals over some media, respectively. This media may be cable wiring or the atmosphere, for example. When communications occur over the atmosphere, or air waves, they are commonly referred to as xe2x80x9cwirelessxe2x80x9d communications. Examples of wireless communications systems include digital cellular, packet data paging, digital cordless telephones, wireless modems, wireless local and wide area networks, digital satellite communications and personal communications networks.
One of the many challenges presented by a wireless communication system is reliable message delivery from a messaging system to a wireless communication device. Herein, from the perspective of the messaging system (e.g., a paging system) the term xe2x80x9cnew messagexe2x80x9d or xe2x80x9cnew fragmentxe2x80x9d will refer to the first copy of an original page or fragment thereof that is transmitted to the wireless communication device (e.g., a pager) and the term xe2x80x9cduplicate messagexe2x80x9d or xe2x80x9cduplicate fragmentxe2x80x9d will refer to a second or subsequent copy of the original page or fragment thereof. From the perspective of the wireless communication device, however, a xe2x80x9cnew messagexe2x80x9d or xe2x80x9cnew fragementxe2x80x9d will refer to the first copy actually received, whether or not it corresponds to the first message/fragment transmitted by the messaging system. Accordingly, the term xe2x80x9cduplicate messagexe2x80x9d or xe2x80x9cduplicate fragmentxe2x80x9d at the wireless communication device refers to a system originated copy of the previously received new message/fragment. Therefore, two original pages that enter the messaging system having the same content are not considered duplicates for purposes of this discussion.
In one-way paging systems, an early approach to increase the chances of successful message reception at the wireless communication device was to transmit multiple copies of each message that entered the paging system. This prior technique is based upon an assumption that most of the time at least one of the repeated copies will be received successfully by the wireless communication device. For its part, the wireless communication device stores received messages and notifies the user of the arrival of each new message. One disadvantage to this early approach was the confusion and frustration caused by the storage and presentation of multiple copies of the same message to the user of the wireless communication device. For example, after having contacted the originator of a message, such as xe2x80x9cPlease call me ASAP,xe2x80x9d it would not be readily apparent to the user whether or not immediate action was necessary when he/she subsequently received a duplicate message that may or may not be a new message.
An improvement over the system above, is illustrated by a voting mechanism which was implemented for use with the Japanese paging system by NEC Corporation and NTT. like the system described above, multiple copies (e.g., a new message and two duplicate messages) of each original page that enter the paging system are transmitted by the paging system. However, in this prior system, logic embedded within the wireless communication device assures only one message is stored on the wireless communication device and presented to the user, thereby eliminating the uncertainty caused by duplicate messages. Upon receipt of all three copies of a particular message and before any errors are known to exist in any of the three messages, the NEC and NTT pagers perform their de-duplication logic on the messages which comprises performing symbol level voting. A majority symbol is selected for each position of the message for a particular message position from among the three messages and a final message is constructed from the selected majority symbols. Although this system improves upon the previous solution to reliable message delivery, many inefficiencies and limitations remain in this type of a compromise system. In some circumstances, construction of an error free message is unrealizable. For example, there may be no majority symbol for one or more symbol positions of the message. Additionally, messages cannot be interleaved in this prior system. That is, the network must send all blocks of a first message prior to sending any block of a second message. This extra complexity in the transmission queuing algorithms results in inefficient channel usage. Further, if a particular message is received correctly in either of the first two copies channel capacity is wasted by transmitting the subsequent message(s).
In light of the foregoing and new flexibility provided by the introduction of two-way communications systems, it is desirable to provide a wireless communication device which is not constrained to a vote among a fixed number of duplicate transmissions. Additionally, it is more efficient for a duplicate message to be transmitted only after it has been confirmed that an error has occurred (e.g., receipt of a message that includes one or more errors at the wireless communication device). Further, it is advantageous to provide a wireless communication device that makes use of the reverse channel available in two-way communications systems to facilitate the correction of garbled messages. More specifically, it is desirable for a wireless communication device to detect garbled messages and provide an indication on the reverse channel that may be used to trigger the transmission of duplicate messages after such detection. It is further desirable for the wireless communication device to distinguish between duplicate messages and new messages and to correct the garbled messages based upon corresponding duplicate messages.
A method and apparatus for detecting duplicate messages and correcting garbled messages in a wireless communication device are described. According to one aspect of the present invention, erred messages received by a wireless communication device are corrected. A first message fragment is received by the wireless communication device. The first message fragment is corrected based upon a second message fragment after it has been determined that the first message fragment contains one or more errors.
According to another aspect of the present invention, a wireless communication device includes a receiver configured to receive messages transmitted over a forward channel from a messaging system; a transmitter configured to transmit responses over a reverse channel to the messaging system; and a processor. The processor is coupled to the receiver to receive messages from the messaging system. The processor is further coupled to the transmitter to transmit acknowledgments to the messaging system. Additionally, the processor is configured to correct garbled messages by determining whether or not a second message is a duplicate of the garbled message. If the second message is a duplicate of the garbled message, then the garbled message is corrected based upon the second message.
Other features of the present invention will be apparent from the accompanying drawings and from the detailed description which follows.